SV40 transcription has been examined after introduction of point mutations in regulatory control regions. These mutants show altered growth properties and differential utilization of promoters. SV40 chromatin complexes are transcribed efficiently and with greater specificity in vitro then is purified SV40 DNA. When purified SV40 is transcribed by purified calf thymus RNA polymerase II there is specificity in initiation and in RNA termination.